Help with Dexter’s rare and serious disease

What I'm about to write is not easy
I know that times are very hard for most of us right now, but there are no other options available to me - Dexter has a very serious disease and his insurance company has caused an issue.

DEXTER’S HISTORY 
I have had Dexter for 9 years and most of those years have been incredibly healthy,  however two years ago he became very  ill with a gastrointestinal disease and unfortunately his insurance at that time had been overlooked and expired when I moved flat.  As a result  I Independently paid the full £2.5 thousand (he was at the royal dick veterinary hospital in ICU for close to a week) that his illness ended up costing. 
Seeing Dexter so close to death during that time meant I immediately purchased for him the best pet insurance I could find with maximum cover as I did not want to be caught out again.

 
I purchased insurance with Insurance Emporium (gold lifetime membership) and this was to provide Dexter with coverage for £6.5 thousand pounds/year with lifetime coverage for chronic conditions. 

THE CURRENT SITUATION
In late 2019 Dexter had his first seizure  and so he went to the vet  for tests (which included a cat scan, EKG and blood panels) and it was during this time it was discovered that Dexter had a lung condition that needed further investigation.
To make a long story short (and after many expensive procedures and treatments) it was discovered that Dexter had caught an extremely rare disease - a type of mycobacteria,  and his lungs were exhibiting lesions. 

Dexter went under the care of a specialist doctor ( a leader in the treatment of this condition) and he was started off with a series of antibiotics (one of these combination antibiotics alone cost £500)… Sadly Dexter had an allergic reaction to this particular medication and despite trying him with antihistamines to control his symptoms of itching ( which was the main side-effects of this drug combination) the poor cat had further seizures and  fainting episodes and we had to stop that Particular treatment Combination .

The next treatment that he was put on is a human medication combination of azithromycin and ethambutol … This was an incredibly frightening time for me because I was terrified that he might experience  complications. Luckily, Dexter has tolerated this combination of medication well. He went for blood tests, an eye examination ( to check for optic neuritis) and an x-ray and thankfully  his blood test came back well within normal limits and his eyes and heart were also fine. So now we have found a triple antibiotic combination that works for darling Dexter which is superb!

Part of his treatment is to ensure that he continues to eat because if he does not maintain his weight he could end up in serious trouble. He is now on an appetite stimulant to help with this. The stimulant  in question ( mitrapazine) is classified as an anti-depressant and it is routinely used for patients of chemotherapy and Dexter has returned to his 100% usual self with small doses of this drug, this again is superb!


So it would seem now that things are cruising along as they should be, I was told that to fight this disease would take approximately 6 months of  triple antibiotic medication and he will require a monthly blood panel to ensure that all is well with his organs.  If he seems to have any stress he can be given supplements to protect his liver and kidney function and periodic X-rays  will be needed to see how his lungs are improving.

THE INSURANCE ISSUE
Dexter’s  insurance was set at £6.5 thousand I did not think that he would be refused this coverage. Imagine my utter shock when I am told by the insurance company that Dexter is not eligible. I challenged the insurance company and had no satisfactory response other than they are using the fact that he had a previous gastrointestinal illness as grounds for "him being more susceptible to this lung infection” and therefore he has had an exclusion put on his cover.
The big problem I have here (Over and above the fact that I now owe over £4 thousand) is that he is a third of the way into his treatment. He must continue to take all of these medications for 3 to 6 more months as It is only with this long-term antibiotic treatment that he can be given a chance to be cured of this awful disease.

WHAT I AM ASKING  HELP FOR
At this stage i am not asking for  help with the current bill, but I am asking for help in my ability to pay for the rest of Dexter’s  treatment At this crucial stage for the duration of this disease.
Naturally if any donations exceed this amount then whatever is in excess will go to pay off the money already accumulated.

(below are two screenshots detailing some of the vet treatment and costS - there are several images and dozens of pages of history so I only included the first and last pages  ...)

I have costed up the remainder of Dexter's treatment - 5 months.

This includes the 3 antibiotics ( Veraflox, azithromycin and ethambutol), the aniti-sickness pills ( cerenia) the appetite stimulator ( mitrapazine) the monthly blood panel and the X-rays . 
The costings are the bare minimum required to get him through the next 5 months, they do not account for any further testing that may need to be done.
However, with luck, the blood tests combined with the x-ray should not cost much above any of this. 

PROGNOSIS 
At the end of the 5 months there will be a clear picture as to how to how successful treatment has been... I cannot try to think too much of what will happen at this point because I can only manage to cope day by day.  It has been Very encouraging in that Dex is enjoying a very happy life and he is Playful and supremely affectionate. Every day I pray that this can continue and that his organs can stand up to this intensive medication regime that he must endure at this time.

WHY HELP DEXTER?
If his medications are to stop it means certain death and I am out of work so I am stuck. I was a successful full time, professional singer but COVID has meant that I have now lost all my work for 2020 and future work beyond that is still uncertain.
 If Dex does not continue  with this full regime of treatment, he will die and he has only just turned 11 he potentially could live for 10 more years, so I must ensure that I do everything I possibly can to help him through this horrendous time.

I staunchly believe that anyone who takes a pet into their life is 100% obligated to ensure that they do everything they can to protect their pet- to treat their pet and to ensure the pets happiness and good health.
I have never failed any of my pets before and I do not intend to now.

Anyone who has met Dexter will attest to his  extraordinary nature, he is very dog-like, extremely affectionate, very social, trusting and very kind.
 During the past 10 nine years I have suffered some extremely sad times; I was diagnosed with fibromyalgia, CFS and I struggle daily with a couple of mental health problems ....and as emotional support, Dexter is my life and my whole world - he Is a constant in my life.  Dex is not "just a cat " - he is my friend. He trusts me implicitly and his health and happiness Is my priority.
In the 9 years I have had Dex he has not once scratched me, slapped me, bitten me, or postured in any such way that it would be ‘normal cat attitude’ - and trust me I know I must've annoyed the crap out of him over these years !. He is an exceptional soul and in honesty I don't foresee that I will ever be able to have another cat after him as no other cat could even come close to the personality that he has…I always say that I won the ‘cat lottery’ when I got Dexter....every night he falls asleep with his head on my chest and hearing his soft little snores is something I cannot bear to be deprived of prematurely.

Thank you so much for taking the time to read this.